An Idiot's Guide to Time

Okay, so this one's going to be a bit odd, but something came up in physics news this week that amuses the hell out of me, so you're just going to have to put up with this.

Time's arrow. A perfectly horizontal line moving from past through present to future. This is how we understand time to work.

If you smash some particles together in an accelerator, they turn into a spray of other particles. If you were to run the movie of that collision backwards – one that showed those other particles forming the original particles – that would, in fact, appear just as valid. This is called time reversal symmetry. Time is basically symmetrical at the quantum level. It's all just particles and energy moving around. And this quantum bullshit dimension contains all the tiny machinery that decides how everything works.

But these people here discovered a subatomic process that doesn't behave in that way. Working in antimatter physics, deep down in the hadronic depths with mesons (tiny buggers, found on a scale several powers tinier than the fields that nanomachines operate in), they found something that wasn't supposed to happen. Down here in the murk, these weird flavours of meson turn into different kinds of stuff all the time. In a world with symmetrical time, the conditions down there say that Thing A will become Thing B more easily than Thing B will turn into Thing A. It's how the reversed movie makes sense.

But it turns out that Thing B turns into Thing A six times more often. This is a bit like reversing a movie of a glass of water being dropped, winding it back to the start – and finding it simply won't go back to the point before the glass tipped over. Time has a preferred direction. Time is asymmetrical.

In fact, you could possibly conceive of time as being a downward slope. Our slide into the future is inexorable. Everything is slipping down time's mountainside.

Makes you wonder what's at the bottom, doesn't it?

This also suggests that time is uphill. The history behind us is on an ever-rising altitude. Maybe ghosts are just clouds of weird electromagnetic spray, caught in the tidal breath of time and drifting downhill into the present day.

People involved in time-travel physics now have to consider that travelling into the past may be, at best, rolling a Sisyphean boulder of conceits up an impossible incline. You know the universe is taking the piss when even the angle of time itself is against you.

There's a beautiful theoretical time machine, envisioned by one Ronald Mallett, that uses a phenomenon called frame-dragging to create, from light, a looping pathway from the present into the future and back again. His idea was that you could step into the beam of light, walk halfway around it, and step out into the future. Rejoin the loop at the same point, and you could walk back to your starting point in the present.

I imagine it now as an endless walk into the future, with all your pasts rising up as a cliff at your back.

Now think about this. Ronald Mallett was set on his own path very early in life. His father died young, of a heart defect. His impetus to think about time travel came from a burning wish to go back in time and warn his father of the undetected condition that would kill him.

Think about that, in a world where time only flows downstream and the past is an unscalable glacier wall. We will hit the bottom of the spiral long before we ever solve the problem of rescuing love or speaking unsaid goodbyes.